Here's exactly what PlayStation VR's mysterious black box does

"It is not extra GPU power for the game."

"It is not more CPU power."

"It is certainly not a PlayStation 4 expansion unit or upgrade."

Chris Norden, Senior Staff Engineer at Sony Computer Entertainment Inc, is talking about the black processing unit that will come with PlayStation VR - and he's annoyed. Annoyed because people keep getting it wrong.

Speaking at GDC 2016, Norden said that he has read and heard people refer to the box as a PS4 GPU upgrade or an "expansion".

"It doesn't do that, that is crazy," he said. "The PS4 is perfectly capable of 120hz output all by itself. It is not an expansion".

So we know what it's not - what does it do?

First off, the PU is responsible for making sure virtual reality sounds as good as it looks. The box does all the object-based 3D audio processing with tech that takes the HRTF (head-related transfer function) and spatialization, along with some other mystery ingredients, to spit out nice 3D audio over any pair of headphones.

Distortion

The box is also responsible for displaying the social screen, which is what appears on the TV. The PU undistorts everything in the picture, undoing all the things that are done when games are made for VR. When you "distort" the picture during development to make it work in VR you lose pixel data, and when you undistort it that data is gone.

So the PU tries to fix the problem by cropping the image and fixing it so it looks as normal as possible - although it's never going to be quite as sharp due to the loss of pixel data.

Third, the box allows for Mirroring Mode and Separate Mode, the latter being where a completely separate audio and visual stream is sent the TV (unlike Mirroring Mode), letting the viewer to see and hear something totally different to the person in the headset.

And finally, the PU responsible for the Cinematic Mode. This means you can use the PS4 for non-VR games while still wearing the headset. You can play PS4 games, watch video, and completely operate the console from within the headset while not in a full VR environment.

So there you have it - that's exactly what the PS VR's Wii-sized friend actually does.

This week, Sony announced that PlayStation VR will cost $399/£349, and confirmed that it will arrive this October. You can read our updated hands-on with the PS VR here.